Preparation Of Hierarchical Porous Carbon Using CaO Template And Its Adsorption Properties For Dyes In Wastewater

The effective treatment of dye wastewater has become a major problem in the field of wastewater treatment.There are many methods of treatment,of which the adsorption method stands out because of its low cost,mild application conditions,and simple operation.And the adsorbent is the core of adsorption technology.Preparation of porous carbon matching the dye properties is the key to the application of activated carbon in dye wastewater treatment.In this paper,the hierarchical porous carbon suitable for dye adsorption is prepared from coal tar pitch with Ca O as the template coupled with KOH activation by adjusting the ratio of carbon source and template.And the surfaces of as-made porous carbons are modified by HNO3 oxidation.The hierarchical porous carbons with nitrogen-containing functional groups were prepared from indole as carbon sources.The BET,FESEM,TEM and XPS were used to analyze the physical structure and surface chemical properties.The adsorption properties of the alizarin green,acid orange 74 and methylene blue dyes with different molecular sizes were investigated.The main results are as follows:(1)The hierarchical porous carbon with lamellar structure was prepared from coal tar pitch with Ca O as the template coupled with KOH activation by adjusting the ratio of carbon source and template.The surface area,average pore size and total pore volume decrease with the increase of template dosing.When the mass ratio of the template to carbon source was 1 with the final activation temperature of 800?,the porous carbon was named HPC2-2-800 with the high specific surface area of 3060 m2/g.As an adsorbent,it has the excellent adsorption properties for all three dyes with different molecular size.For the alizarin green and methylene blue,the Langmuir model fits well,and the correlation coefficient is about 0.99.The adsorption of alizarin green and methylene blue by HPCs is mainly monolayer adsorption,and the maximum adsorption capacity is 1484 mg/g and 1149 mg/g,respectively.For acid orange 74,the Freundich model can be better to describe its adsorption behavior.Kinetic studies show that the adsorption process of HPCs on alizarin green and acid orange 74 accords with the first-order model,and the adsorption behavior of HPCs on methylene blue conform to the pseudo-second-order model.(2)The as-made hierarchical porous carbon was modified by HNO3 oxidation to increase the surface acid concentration of oxygen-containing functional groups.And its adsorption properties for basic dyes were investigated.The surface oxidation carbon still keeps the lamellar structure with decreasing the specific surface area;however,the some acidic oxygen-containing functional groups have been introduced.Compared with the original carbon,the adsorption properties of methylene blue on the modified porous carbon has been improved due to the increase of polarity and hydrophilicity,however,the adsorption properties of alizarin green is slightly decreased on the modified porous carbon because alizarin green is organic dye.From the isotherm model,the Langmuir model can better describe the adsorption process of methylene blue with the maximum adsorption capacity is 1295 mg/g,while the adsorption process of alizarin green is more consistent with the Freundich model.The kinetic results show that alizarin green and acidic orange 74 accord with the pseudo first order kinetic model,while methylene blue conforms to the pseudo second order kinetic model.(3)The lamellar hierarchical porous carbon with nitrogen-containing functional groups were made from indole with Ca O as the template coupled with KOH activation by adjusting the final activation temperature.The surface area increases with the increase of final activation temperature.When the final temperature was 900?,the specific surface area is up to 1629 m2/g,indicating that high temperature was beneficial to the pore formation of porous carbon.The results of adsorption for dyes show that the as-made carbon has very high adsorption capacity for acid dye due to the introducing of nitrogen-containing functional groups even in the very low concentration of dye.And the Freundich model is more suitable for describing the adsorption process of alizarin green and acid orange 74.The kinetic results showed that the acid orange 74 met the pseudo first-order kinetic model,while the alizarin green conformed to the pseudo-second-order kinetic model.